Abstract

An X-ray single-crystal structural investigation on a sample of cancrinite of formula Na7.13Ca0.87(Si6Al6O24) (SO4)0.07(CO3)1.43 2H2O has been carried out. The cancrinite cage content has been found to be similar to that reported in previous structure refinements on natural and synthetic samples. However, differently from reference data, cations located inside the uninterrupted channel are distributed between two independent sites M1 and M2. Moreover carbonate groups are distributed, with partial occupancy, between two different z elevations (Cl-OC1 and C2-OC2). The tetrahedral co-ordination of the sulphate group is obtained by partial substitution of carbon atoms at C1 and C2 by sulphur and oxygen. Two possible orientation with the apical oxygen pointing “down” or “up” are possible.

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